Conventionally, there has been a PLL circuit in which a phase comparator, a charge pump circuit, a loop filter and a VCO are provided, and which outputs an output signal synchronized with a phase of an input frequency signal.
In the PLL circuit, particularly in the charge pump circuit, there is a case where noise such as flicker noise and thermal noise is superimposed on an output signal.
For example, the charge pump circuit includes a current mirror circuit, and there is a case where noise generated at a mirror source is superimposed on a current at a mirror destination in accordance with a mirror ratio. If a size of a mirror source transistor is made larger, a current flowing in the mirror source transistor is increased, and a mirror ratio is decreased, it is possible to suppress noise at the current mirror circuit.
While it is possible to suppress noise by making a size of the charge pump circuit larger, there is a problem that it is difficult to make the size smaller while trying to suppress noise.